Advertising
Search term
What a person actually typed, as opposed to the keyword the advertiser bid on that matched it.
What makes it wrong.
The mechanism, not the warning.
The report does not show every term. Terms below a volume threshold are withheld for privacy, so the terms shown never sum to the campaign total, and the withheld tail can hold a meaningful share of the spend.
In detail.
Keywords are bids, search terms are reality. Broad and phrase matching mean one keyword collects many terms, some of which have nothing to do with the intended intent.
The search terms report is where wasted spend is visible, and it is the input to negative keywords.
Where this is measured.
Search term comes from Google Ads. The server page lists every tool that returns it, with its parameters.